As examples of metallic elbows for a pipe, there are known a casted elbow formed with a die, an elbow formed by bending a straight pipe, a welded elbow formed by integrally but-welding two halved bent pipe materials obtained by pressing a metal plate, and a machined elbow formed by cutting a metal material.
Of those, the machined elbow is given in, for example, Patent Literature 2 below. Further, Patent Literature 1 below describes the elbow formed by bending and the welded elbow.